1. Technical Field
The present disclosure relates to phase change memories (PCMs).
2. Description of the Related Art
Phase change materials have at least two phases: a crystalline phase, and an amorphous phase. A phase change memory uses phase change materials as storage elements therein (hereinafter named phase change storage elements). A crystalline phase is represented as logic ‘0’ and an amorphous phase is represented as logic ‘1’.
The transformation between the crystalline phase and the amorphous phase is controlled by an operating current flowing through the phase change storage element. Table 1 is a comparison of operating current for a crystalline phase and an amorphous phase.
TABLE 1Comparison of write current for a crystallinephase and an amorphous phase.Operating current (in pulse form, oscillatingbetween high and low voltage levels)magnitudeduty periodcrystalline phaseLowLongamorphous phaseHighShortAchieving complete crystallization is difficult. For example, an inappropriate operating current may result in incomplete crystallization, which affects reliability of the phase change storage element.